1. Field of the Invention
The present invention relates to a surface acoustic wave device used for a resonator, a band pass filter, or other suitable devices.
2. Description of the Related Art
Heretofore, a surface acoustic wave device that utilizes a surface acoustic wave has been widely used as, for example, a resonator or a filter device. For example, in Japanese Unexamined Patent Application Publication No. 2001-44787, as one example of such a surface acoustic wave device, a surface acoustic wave device is disclosed which includes a SiO2 film formed on a piezoelectric substrate so as to cover an IDT electrode and a SiN film formed on the SiO2 film.
As a result of the SiO2 film being formed so as to cover the IDT electrode, the surface acoustic wave device disclosed in Japanese Unexamined Patent Application Publication No. 2001-44787 has excellent frequency temperature characteristics. In addition, in the surface acoustic wave device disclosed in Japanese Unexamined Patent Application Publication No. 2001-44787, when the thickness of the SiN film formed on the SiO2 film is adjusted, the frequency characteristics of the surface acoustic wave device can be adjusted. Thus, the frequency accuracy can be improved.
However, in the surface acoustic wave device disclosed in Japanese Unexamined Patent Application Publication No. 2001-44787, for example, spurious response may be disadvantageously generated between a resonant frequency and an anti-resonant frequency or in a passband due to an unnecessary wave.